[time-nuts] Wavecrest DTS-2077 Teardown
Ed Palmer
ed_palmer at sasktel.net
Wed Aug 21 16:44:24 EDT 2013
Since you're looking for rise times in the low or sub nanosecond range,
why wouldn't you include any logic gates where such rise times are
inherent? I was thinking of maybe a chain of faster and faster logic
gates. For example, Potato Semiconductor - no, I'm not making that up -
PO74G04A has a risetime of < 1 ns and, if you can keep the load
capacitance low enough, a maximum input frequency of > 1 GHz.
Always trying to learn....
Ed
On 8/20/2013 11:28 PM, Bruce Griffiths wrote:
> The same analysis applies however one would probably use something
> like cascaded longtailed pairs with well defined gain (series emitter
> feedback) and the low pass filter cap connected between the collectors
> rather than opamps.
>
> Bruce
>
> Ed Palmer wrote:
>> Does anyone know if this situation would benefit from doing something
>> similar to a 'Collins Hard Limiter' i.e. instead of squaring the
>> signal in one stage, use maybe two or three cascaded stages with
>> increasing bandwidths? Normally, Collins limiters are used with beat
>> frequencies of less than 1 KHz, but maybe there's value in doing at
>> typical time-nuts frequencies.
>>
>> Any thoughts?
>>
>> Ed
>>
>>
>> On 8/20/2013 10:02 PM, Said Jackson wrote:
>>> Hi Ed,
>>>
>>> For anything up to about 150MHz try the NC74SZ04 types from National
>>> if you can find them NOS. they stopped making these years ago..
>>> Fairchild is ok too but not as fast from what I have seen.
>>>
>>> Forgot I wrote about it in 2009. Oh boy -age kicking in.
>>>
>>> Bye,
>>> Said
>>>
>>> Sent From iPhone
>>>
>>> On Aug 20, 2013, at 20:17, Ed Palmer <ed_palmer at sasktel.net> wrote:
>>>
>>>> Hi Said,
>>>>
>>>> Yes, I saw your message from 2009 where you warned about the sine
>>>> waves. That's why I was watching for it. Thanks for the warning.
>>>> I also realized that a DC Block and a 10 db attenuator makes a very
>>>> nice TTL or CMOS to Wavecrest converter for anything except 1 PPS
>>>> which would need about 15 db. I tried an old circuit that uses an
>>>> MC10116 ecl line receiver - it's actually a dead Racal Dana 1992
>>>> counter where I'm using the processing on the external reference
>>>> input to square up the signal. It gives me a slew rate equivalent
>>>> to about a 50 MHz sine wave. It helped a lot, but not enough.
>>>> I'll try a 74AC04 and a BRS2G Differential Line Receiver (risetime
>>>> < 3ns, 400Mbps throughput). Both are in my junkbox.
>>>>
>>>> Ed
>>>>
>>>>
>>>> On 8/20/2013 8:12 PM, Said Jackson wrote:
>>>>> Guys,
>>>>>
>>>>> The dts needs to be driven by square waves, driving them with sine
>>>>> waves gives jitter values that are displayed significantly too
>>>>> high due to trigger noise.
>>>>>
>>>>> Holzworth makes a small sine wave to square wave converter that
>>>>> can drive 50 ohms. Use a DC block and an attenuator on the cmos
>>>>> output to avoid damaging the dts inputs. You can make your own
>>>>> converter using a single fast cmos gate, resistor, and blocking
>>>>> cap. By using hand-selected gates I was able to achieve less
>>>>> jitter with that circuit than what the Holzworth box was able to
>>>>> achieve.
>>>>>
>>>>> Doing that conversion can bring down the measured rms jitter on a
>>>>> very good 10MHz sine wave source from 10ps+ to less than 2ps -
>>>>> basically at or below the noise floor of the dts.. Once you run at
>>>>> the units' noise floor, you know your source is quite good..
>>>>>
>>>>> Bye,
>>>>> Said
>>>>>
>>>>> Sent From iPhone
>>>>>
>>>>> On Aug 20, 2013, at 18:51, Ed Palmer <ed_palmer at sasktel.net> wrote:
>>>>>
>>>>>> Adrian,
>>>>>>
>>>>>> I used Timelab to assess the reaction of the DTS-2077 to
>>>>>> different sine wave inputs. The differences in the noise floor
>>>>>> are surprising. The attached picture was made by taking the
>>>>>> output of an HP 8647A Synthesized Generator through a splitter,
>>>>>> and then through different lengths of cables to the inputs of the
>>>>>> DTS-2077. The combination of splitter and cable loss meant I
>>>>>> couldn't get +7 dbm @ 1 GHz. If I could have, the 1 GHz line
>>>>>> might have been lower than it was.
>>>>>>
>>>>>> Ed
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